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Re: Question regarding XFS on LVM over hardware RAID.

To: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Subject: Re: Question regarding XFS on LVM over hardware RAID.
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 3 Feb 2014 08:21:52 +1100
Cc: "C. Morgan Hamill" <chamill@xxxxxxxxxxxx>, xfs <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <52ED61C9.8060504@xxxxxxxxxxxxxxxxx>
References: <1391005406-sup-1881@xxxxxxxxxxxxxxx> <52E91923.4070706@xxxxxxxxxxx> <1391022066-sup-5863@xxxxxxxxxxxxxxx> <52E99504.4030902@xxxxxxxxxxxxxxxxx> <1391090527-sup-4664@xxxxxxxxxxxxxxx> <20140130202819.GO2212@dastard> <52EB3B96.7000103@xxxxxxxxxxxxxxxxx> <1391202273-sup-9265@xxxxxxxxxxxxxxx> <52ED61C9.8060504@xxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Sat, Feb 01, 2014 at 03:06:17PM -0600, Stan Hoeppner wrote:
> On 1/31/2014 3:14 PM, C. Morgan Hamill wrote:
> > So, basically, --dataalignment is my friend during pvcreate and
> > lvcreate.
> If the logical sector size reported by your RAID controller is 512
> bytes, then "--dataalignment=9216s" should start your data section on a
> RAID60 stripe boundary after the metadata section.
> Tthe PhysicalExtentSize should probably also match the 4608KB stripe
> width, but this is apparently not possible.  PhysicalExtentSize must be
> a power of 2 value.  I don't know if or how this will affect XFS aligned
> write out.  You'll need to consult with someone more knowledgeable of LVM.

You can't do single IOs of that size, anyway, so this is where the
BBWC on the raid controller does it's magic and caches sequntial IOs
until it has full stripe writes cached....


Dave Chinner

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